Embodiments of the present invention generally relate to implantable cardiac devices, and more particularly to intra-pericardial medical devices having a built-in telemetry system.
Implantable medical devices, for example, pacemakers, cardio-defibrillators, neurostimulators and the like, utilize leads to form the electrical connection between a device pulse generator and tissue or nerves that are to be stimulated. As is well known, the leads connecting such devices with the heart may be used for pacing or for sensing electrical signals produced by the heart, or for both pacing and sensing in which case a single lead serves as a bidirectional pulse transmission link between the device and the heart. The lead typically comprises a distal end portion for carrying a tip electrode and a ring electrode. The lead may also carry one or more cardioverting and/or defibrillation shocking electrodes.
Various lead types for different placement approaches have been developed, including endocardial and epicardial leads. For example, an endocardial type lead is one that is inserted into a vein and guided therethrough to a target location, for example, in one or both of the chambers of the right side of the heart or within one of the veins of the coronary sinus region of the heart for left side stimulation and/or sensing. The distal end portion of an endocardial lead may carry a helical, screw-in tip element, electrically active or inactive, and/or outwardly projecting tines or nubs and/or a sinuous shape for anchoring the lead.
There are factors, however, which warrant alternatives to a transvenous lead. These factors include coronary sinus and/or coronary venous obstructions. Furthermore, the location of the coronary veins effects the implant location of the electrode, which can make it difficult to place a left side lead in a specific preferred location and may lengthen or render unpredictable the amount of time needed to implant the lead. In addition, a portion of the patient population is unable to receive this type of lead due to vasculature anomalies. In such cases, epicardial or myocardial type leads may be used. Such leads are attached directly to the epicardium using sutures or other fixation mechanisms such as a helical screw-in electrode that engages the myocardium. Myocardial leads typically are used for temporary pacing or for permanent pacing following open-heart surgery.
Conventional approaches to the placement of epicardial leads usually involve thoracotomies or sternotomies. Such placement techniques have disadvantages.
To mitigate these disadvantages, minimally invasive lead placement techniques have been developed for placing a myocardial lead on the surface of the heart via a small, finger size opening in the chest. Such techniques may include the use of a fiber optics video camera of the type commonly used in other thoracic surgeries (for example, lung biopsies and other thoracic cavity and cardiac procedures) for visually imaging, and thereby aiding, the lead placement procedure. These minimally-invasive lead placement techniques allow for faster, safer and easier myocardial lead placements with significantly less morbidity, trauma and pain to the patient. Percutaneous access to the epicardial surface comprises an even less invasive technique, available not only to surgeons but to cardiologists as well.
Moreover, cardiac leads for conventional implantable medical devices experience at least some of the following limitations. Conventional cardiac leads afford limited access to only certain locations of the left atrium (LA) and left ventricle (LV) that are depend in part on vein location. Conventional cardiac leads are limited to pacing/sensing based timing for only certain combinations of electrodes due to the electrodes proximity to the RA, RV, LA and LV. Further, conventional cardiac leads create RF heating sources when in the presence of an MRI field if not corrected through added structure or circuits which increase size, complexity, cost and the like. Also, conventional cardiac leads, through their size and placement inside the myocardium, form conducting paths or loops that result from an antenna effect caused when the leads experience an RF field. Conventional cardiac leads, through their size and placement inside the myocardium, experience Eddy current flow that creates a risk of heating and cardiac stimulation. Further, conventional implantable medical device (IMD) systems may experience large forces and torques imposed thereon. These forces cause an undue risk of lead fracture near where the lead passes by the clavical bone. As the patient moves over time, the clavical bone wears on the lead and may fracture the lead.
There is a desire to move towards a satellite pacing system as a potential future trend for less mechanical lead issues and MRI safety. Satellite pacing systems are appealing, but thus far have faced various challenges in implementation, such as for dual chamber pacing or atrio-ventricular (AV) synchrony. For example, it has been proposed to provide a satellite pacing system having one or more slave pacing components located on or in the heart and a master pacemaker controller located where a conventional IMD is positioned. The slave pacing components include a sensing and pacing electrode(s) located at a desired position about the heart. The slave pacing components communicate with the master pacemaker controller. The master pacemaker controller represents a conventional pacemaker or implantable cardioverter-defibrillator (ICD). In this proposed satellite pacing system, conventional leads are not useable.
However, this master/slave configuration has experienced certain difficulties. As one example, the communications link to the slaves is difficult to maintain and use an undue amount of power to maintain.
There remains a need for an improved implantable medical device.